1. Field of the Invention
The present invention relates to network control device and control method and a program thereof and, more particularly, to network control device and control method and a program thereof which enable efficient execution of linkage between distributed services while reducing physical constraints on the network.
2. Description of the Related Art
In recent years, as network communication systems including the Internet have been put to commercial use, it becomes a common practice for individuals to use the Internet not only at offices but also at home. We are now at the stage of embodying establishment of a system (ubiquitous computing) which enables numbers of conventionally isolated various kinds of apparatuses to use self-contained computer resources with each other through a network, thereby providing more facility as a whole.
As topology in networks including the Internet, bus topology and ring topology are well known. In bus topology, signals are transmitted in both ways on a bus, while in ring topology, they are transmitted in one way on a closed loop cable.
A sub-network node connected to the network transmits information onto a network line, as well as taking in information related to each equipment connected to the node in question from the information transmitted through the network line.
With reference to FIGS. 10 and 11 which show one example of a mode of connection between a sub-network and a network control device, with the above-described conventional network system, although a distributed service in which the entire system is divided into some of highly independent functional units to distribute and arrange each functional unit at an optimum machine had been used in a closed form within the same kind of sub-networks, sharing of information has been conducted with network connection provided between these sub-networks.
Moreover, as the next step, there arises the need of distributed services between different kinds of sub-networks as a higher degree of freedom.
In order to meet the need, as shown in FIGS. 10 and 11, it is a conventional practice to connect sub-networks which should be connected by a gate way that serves for the connection to another host via its connected host computer, as well as individually executing conversion of messages inherent to the relevant sub-networks to/from each other.
The example shown in FIG. 11 is recited, for example, in Japanese Patent Laying-Open (Kokai) No. Heisei 11-215174.
The system recited in the literature aims at using, from a certain network, a network of a system of a kind different from the network without being conscious of the system of the partner network.
As described above, since in the conventional network communication system, sub-networks which should be connected are connected by a gate way that serves for the connection to another host via its connected host computer, while conversion of messages inherent to the relevant sub-networks to/from each other is individually conducted, such a case where the number of different kinds of sub-networks to be connected therebetween is small could be coped with by the application of this method.
Because most of the conventional systems have such a simple sub-network structure, no more special measure has been required.
With an increase in the number of sub-networks and a following increase in the volume of service traffic which is information transmitted and received through a network, however, the volume of processing at a gate way portion has been increased. In addition, when a conventional method is applied, physical constraints such as network wiring have become heavier depending on a system to which the method is applied.
More specifically, problems in conventional art are as follow. First problem is that in a method where sequential conversion is conducted when services belonging to sub-networks having different kinds of network architectures link through a plurality of sub-networks, service directory management of managing message conversion and information and providing a user with the information and management of packet routing for selecting the best packet from a set of data sectioned to have a fixed size are complicated.
As a result, overhead during processing is increased to consume more resources, while a throughput of the network system is reduced.
The reason is that with no protocol indicative of a procedure for service management common among a plurality of sub-networks defined, an inherent service management protocol is already mounted. Another reason is that in terms of successiveness, there are many cases where mounting a completely new and common service management protocol gives no solution.
Second problem is that multi-stage message conversion increases a management overhead for guaranteeing its completeness and reversibility.
The reason, which is common to the first reason, is that since a sub-network as a target here is each mounted with its inherent service management protocol, setting of a protocol for executing general abstraction layer fails to function effectively.